I've shipped lots of small mechanical devices and parts with no trouble and no questions asked all over the world. If you announce to one and all that there's a gun in here then in my humble opinion you are asking for it to be stolen.
Understand, I've never sent a gun anywhere nor received one via common carrier so my real world experience is limited. But I can't imagine a criminal following all these shipping rules if they want to get a gun from here to there. Just pack it, ship it and if it gets there, great! If it doesn't, then get another gun and repeat.
It just seems like another case of people who are overly concerned with rules making a few too many.
Just my 2c worth.